1. Field of the Invention
The present invention relates to a coil unit and a wireless power transmission device.
2. Description of the Related Art
Recently, in order to transmit power without mechanical contact by a cable or the like, a wireless power transmission technique using electromagnetic induction operation between a primary (transmission) coil and a secondary (power receiving) coil which face each other has attracted attention, and is expected to be widely used as a power feeding device for charging a secondary battery mounted in an electric vehicle (EV) or a plug-in hybrid electric vehicle (PHEV).
In a case in which a wireless power transmission technique is applied to a power feeding device for an electric vehicle or the like, it is assumed that a positional relationship between a transmission coil provided on the ground and a power receiving coil mounted in an electric vehicle or the like is not necessarily constant. In this way, in a case in which the positions of the transmission coil and the power receiving coil are shifted, magnetic coupling between the coils is significantly reduced, and as a result, there is a problem in which power transmission efficiency is reduced.
In Japanese Unexamined Patent Application Publication No. 2010-172084, a technique of a non-contact power feeding device using a plurality of cores disposed at predetermined intervals on a flat surface has been proposed. Japanese Unexamined Patent Application Publication No. 2010-172084 discloses that the non-contact power feeding device is resistant to a positional shift since the plurality of cores operate as cores with sizes expanded by including a gap therebetween.
In the technique disclosed in Japanese Unexamined Patent Application Publication No. 2010-172084, the plurality of cores are disposed at predetermined intervals on a flat surface, each core using a coil in which a winding wire is wound in a helical shape, and thus power transmission efficiency can be increased. However, in a case of the coil in which a winding wire is wound in a helical shape into the cores, since a magnetic flux which is circulated up to a place separated from the coil is easily generated, there is a problem that an unnecessary leakage magnetic field is easy to be formed in the place separated from the coil. Particularly, in a case in which a wireless power transmission technique is applied to a charging device for a power electronic device such as an electric vehicle, since it is necessary to make a large current flow through the coil because a large power transmission is required, there is a possibility that a leakage magnetic field strength formed in the place separated from the coil may also increase, and electromagnetic interference negatively affecting a peripheral electronic apparatus or the like may occur.